A typical circuit design implemented on a printed circuit board contains parts such as transistors, resistors, capacitors and integrated circuits. Assembly of circuit designs on printed circuit boards is a favored industry practice because it permits low-cost production and easy maintenance.
It is not unusual for a circuit design implemented on a printed circuit board to contain one or more vibration sensitive components, for example, a voltage controlled oscillator or resonant circuit, in addition to supporting circuitry. Furthermore, it is not unusual for a printed circuit board containing a vibration sensitive circuit or component to be placed in an environment that subjects the board to external vibration forces in an axis perpendicular to the plane of the board, for example, placement of the circuit board in an automobile or airplane. When oriented in this manner, external vibration forces can cause deflections in the circuit board that influence the operation of vibration sensitive components attached thereto.
As the printed circuit board vibrates and deflects, a small part of the shunt capacitance between the circuit component leads and the ground plane varies in concert with the vibrational motion. Board deflection and the associated shunt capacitance variation are most severe at or near the natural resonance frequency of the printed circuit board. As is well known, this variation in shunt capacitance often causes a corresponding variation in the output oscillation frequency of vibration sensitive components or resonant circuits mounted to the vibrating circuit board.
Local oscillators used in telecommunications equipment are most susceptible to the effects of circuit board vibration and deflection. Deviations in the local frequency of oscillation caused by shunt capacitance variation resulting from circuit board vibration and deflection corrupts the output spectrum of the local oscillator. Corruption of this kind is known as incidental frequency modulation and manifests itself as phase jitter when measuring data signals. In conclusion, variable shunt capacitance effects from vibrating and deflecting circuit boards can render sophisticated and important vibration sensitive circuitry unusable or unreliable in hostile environments.
Accordingly, there is a need for an improved mounting of vibration sensitive circuit components on printed circuit boards to minimize the effects of external vibration sources on vibration sensitive circuit components.